Magnetic disk drives for use as the external storage devices of information-processing apparatuses such as computers are required to have higher recording capacities, and are therefore improved primarily in recording density in order to meet this requirement. Enhancing density by using a conventional longitudinal magnetic recording scheme, however, poses the problem that since a large diamagnetic field occurs in the transition region of magnetization on the medium, reduction in the recording layer film thickness thereof is required and recorded data is consequently lost by thermal confusion. Meanwhile, for the perpendicular magnetic recording scheme where a recording magnetization process for the medium is conducted in its film thickness direction, high recording density is easy to achieve, since the diamagnetic field occurring in the magnetization transition region is small and thus since the necessity for the reduction in the film thickness of the medium is not too substantial.
When a signal is recorded on a perpendicular recording medium by using a perpendicular recording magnetic head, the electrical signal is converted into a magnetic signal by a coil and thus the main and subsidiary magnetic pole pieces of the head are excited to generate magnetic fluxes. Part of these magnetic fluxes flow from the subsidiary magnetic pole piece and after moving past the area between the main and subsidiary magnetic pole pieces, penetrate the perpendicular recording layer of the recording medium. After this, a closed loop is formed that returns to the subsidiary magnetic pole piece through the soft magnetic underlayer located below the perpendicular recording layer. At this time, the subsidiary magnetic pole piece is used to return the magnetic fluxes that have occurred at the perpendicular recording layer and soft magnetic underlayer of the recording medium, from the main magnetic pole piece to the subsidiary magnetic pole piece efficiently and magnetically. The magnetic fluxes flow in this manner to record a magnetizing signal on the perpendicular recording medium.
To improve recording density in the perpendicular recording scheme, it is necessary to process the element height of the read head and that of the write head very accurately. Japanese Patent Publication No. 2006-48806 (“Patent Document 1”) describes a technique that allows both the element height (throat height) of a write head and the element height (sensor height) of a read head to be controlled by using the procedure below. First, a special detection pattern for air bearing surface processing of the read head and a special detection pattern for air bearing surface processing of the write head are provided in respective sections that operate as sliders. Next, the air bearing surface of the write head is lapped while the element height (throat height) thereof is being monitored by using the detection pattern for air bearing surface processing, and during this monitoring process, the special detection pattern for air bearing surface processing of the read head as well is monitored. It is also described that during air bearing surface lapping of the write and read heads, the resistance values of the processing detection patterns for the heads are checked and if the throat height of the write head is found to be large in comparison with the sensor height of the read head, the air bearing surface of the write head is lapped at a tilt to reduce the throat height thereof.
Japanese Patent Publication No. 2005-317069 (“Patent Document 2”) describes a technique that the processing accuracy of throat height TH as well as that of magnetoresistive (MR) element height can be enhanced by using the procedure below. First, on the air bearing surface of a bar, a plurality of first resistive films are provided at the same layer positions as those of the MR element, and a plurality of second resistive films are provided at the same layer positions as those of a recording gap. Next, the resistance values of the first and second resistive films are measured while the air bearing surface of the bar is being lapped, and the amounts of lapping of the air bearing surface in a longitudinal direction and minor-axis direction thereof are controlled on the basis of the respective resistance values of the first resistive films and those of the second resistive films.
Japanese Patent Publication No. 2000-67408 (“Patent Document 3”) describes a technique in which, during the lapping of a read head such as an MR head or giant MR head, a first ELG (Electrical Lapping Guide) element larger than the read head in element height and a second ELG element of the same shape as that of the read head are provided. Then the element height of the read head is controlled to be a required dimensional accuracy while being monitored with the first ELG element, and the element resistance value of the read head is controlled to be a required value while being monitored with the second ELG element.
In the above conventional techniques, the throat height of the write head and the sensor height of the read head are controlled by measuring the resistance values of the ELG elements (processing detection patterns) that are correlated with the throat height and the sensor height. There is the problem, however, that since the write head ELG element patterning of the perpendicular recording magnetic head is conducted by ion milling primarily from the air bearing surface side of the write head simultaneously with the formation of the main magnetic pole piece, swarf by ion milling re-sticks to the edge opposite to the air bearing surface of the ELG element and makes the resistance value of this ELG element unstable. If the resistance value of the ELG element becomes unstable and nonuniform, lapping the throat height section of the main magnetic pole piece that is required to be dimensionally accurate cannot be controlled with high accuracy.
Since the front end positions of the write ELGs of a perpendicular recording magnetic head are determined during ion milling from the air bearing surface side simultaneously with the formation of the main magnetic pole piece, fragments of the material lapped will re-stick to the edge at the opposite side to the air bearing surface of each ELG, resulting in unstable ELG resistance values. The instability and nonuniformity of ELG resistance values do not make highly accurate lapping control of the throat height of the main magnetic pole piece.